Fatty acids and alkyl esters thereof are the building blocks for various compositions ranging from lubricants, polymers, solvents, cosmetics and the like. Fatty acids are generally obtained by hydrolysis of triglycerides of vegetable or animal origin. Naturally occurring triglycerides are esters of glycerol and generally straight chain, even numbered carboxylic acids, in size ranging from 10-24 carbon atoms. Most common are fatty acids having 12, 14, 16 or 18 carbon atoms. The fatty acids are either saturated or contain one or more unsaturated bonds.
Long, straight chain saturated fatty acids (C10:0 and higher) are solid at room temperature, which makes them difficult to process in a number of applications. Unsaturated long chain fatty acids, however, e.g. oleic acid are liquid at room temperature, so are easy to process, but are unstable because of the existence of double bond(s). Branched fatty acids mimic the properties of the straight chain unsaturated fatty acids in many respects, but do not have the disadvantage of being unstable. “Branched fatty acids” means fatty acids containing one or more alkyl side groups, and/or aryl groups, which are attached to the carbon chain backbone at any position. Therefore, branched fatty acids are for many applications more desirable than straight chain fatty acids. Commercial branched acids are not, however, naturally occurring materials.
In one process U.S. Pat. Nos. 5,440,059 and 5,840,942 describe the reaction of xylene and oleic acid using acidic clay as catalyst. Clay to oleic ratio (wt/wt) is from 2 to 0.6; xylene to oleic ratio (wt/wt) is up to 20. The reaction temperature range is from 130-250° C., but large amount of dimer and heavy acids were formed at high temperature.
Kohashi's paper (JAOCS, Vol. 61, no. 6, June 1984) showed that acidic clay also catalyzes the addition of phenol to oleic acid, but the reaction of toluene with oleic acid was very slow to catalyze.
U.S. Pat. No. 5,840,942 discloses a method for preparing an aryl-substituted fatty acid or fatty ester. The method involves the use of zeolite or certain clay catalysts. The clay catalysts are acid clay catalysts of the type known for their usefulness in dimmer acid synthesis.
Finally, U.S. Pat. No. 5,034,161 discloses reactions between toluene, xylene, phenol and oleic acid catalyzed by Nafion catalyst NR-50, available from E.I. du Pont. The Nafion catalyst is believed to be a perfluorinated resin treated with sulfonic acid.
However, all of these processes are plagued by low yield and/or a high rate of undesirable byproduct formation. Accordingly, there is a need for an improved process that overcomes these disadvantages, i.e. a process for the preparation of aryl branched fatty acids from straight chain unsaturated fatty acid feedstocks comprising at least one aryl compound with a high conversion rate, an increased selectivity towards branched monomeric isomers and which employs a reusable catalyst.